Kevin Ward Jr., a 20-year-old race car driver, was killed Saturday night after he was struck on the track by NASCAR star Tony Stewart, according to Ontario County (N.Y.) Sheriff Philip C. Povero.

During a sprint car race at Canandaigua (N.Y.) Motorsports Park, Ward was spun out by Stewart, got out of his car to show his displeasure and then was struck by Stewart's car, sending Ward sliding down the track, fellow sprint car racer Tyler Graves and witness Adam Dulski told USA TODAY Sports.

Povero confirmed the driver was taken by ambulance to Thompson Health and was pronounced dead on arrival.

The Ontario County Sheriff's Department confirmed the dead driver's identity later Sunday morning.

"This is an ongoing investigation of an on-track crash," Povero said.

Povero indicated Stewart, 43, was ''fully cooperative'' and that the incident is not being investigated as a criminal matter.

The sheriff's department said the cars involved were taken to private garages.

"Next is continuing interviews, a continued evaluation of evidence we have, including video, and there is certainly going to be an evaluation of medical evidence when it is collected from the autopsy," Povero said.

Mike Arning, a spokesman for NASCAR team Stewart-Haas Racing, which Stewart co-owns, issued the following statement:

"A tragic accident took place last night during a sprint car race in which Tony Stewart was participating. Tony was unhurt, but a fellow competitor lost his life. Our thoughts and prayers go out to his family and friends. We're still attempting to sort through all the details and we appreciate your understanding during this difficult time."

NASCAR did not respond to USA TODAY Sports' request for comment.

The Ontario County Sheriff's Department confirmed deputies were on the scene and investigating an incident at the track before Povero spoke with the media around 3 a.m. Sunday morning.

Ward, who raced the No. 13 sprint car at the track, started racing go-karts in 1998 at 4, according to kevinwardracing.com.

Coming out of Turn 2, Stewart's car squeezed Ward's car up into the outside wall, turning it around. Ward's car had a flat tire as a result, and he exited the car to show his displeasure with Stewart's move. He marched down the track and was pointing at Stewart's car as he approached on the ensuing caution lap. Stewart's car then clipped Ward, who was run over and thrown a few yards down the track.

"It happened in Turn 2," said the 27-year-old Dulski. "The prior lap, Tony had gotten into him – just spun him, nothing big, just spun him around. The caution came out. He hopped out of the car – the driver of the 13 ... he hopped out to go and yell and point a finger at Tony, typical thing.

"Tony came around ... the back end slid out, and he definitely caught him – I couldn't tell if it was with the front or the back of the car. ... The body made contact with the car and went sliding across the track. It was the worst thing I've ever seen."

Graves, 16, of Bolivar, N.Y., said he "grew up watching Kevin the last couple years, then I made the move to sprint cars. I now race a 360. I've raced alongside with Kevin the past two years. …

"Tony and Kevin were battling. … I believe they got together on the frontstretch, Kevin hit the wall and his tire went down. So he spun between (turns) 1 and 2. He got out of the car after the caution was thrown and began to walk down the track, pointing right at the 14, throwing his hands all around. The last thing I seen Kevin do was put his finger to his helmet."

Graves said he saw Ward caught up under the tire and then launched a few yards down the track. Ward hit the ground and didn't move, according to Graves.

Barbara Manning, a nursing supervisor at Thompson Health, said Ward's mother and two sisters went to the hospital after the incident.

"I know that the racing community is a very close family," Manning said. "This is an unfortunate tragedy, but they will pull together. They love the sport and know the risks involved. He was so young and had a very big career ahead of him."

According to Ward's website, he started driving sprint cars in 2010 when he notched five top-five finishes. In 2012, he was named Empire Super Sprint rookie of the year. This season was his fifth racing the Empire Super Sprints.

Stewart, a three-time Sprint Cup champion who suffered a compound fracture of his right leg in a sprint car accident a year ago, had just returned to the hobby he says helps fuel his success in NASCAR.

After Saturday night's incident, racing was canceled for the rest of the night, according to the track's Facebook page.

In a later post, the track said: "Canandaigua Motorspots Park will not have an official statement on the accident that happened in the ESS race until tomorrow. Please pray for the entire racing community of fans, drivers, and families. Please be respectful in any comments."

Tony Stewart expressed his excitement for his final Sprint Cup season, Jan. 21 during NASCAR media week, but two weeks later, Stewart-Haas Racing announced the driver would miss the beginning of the season after breaking a vertebra in his back in an ATV accident.
Mike McCarn, AP

Kevin Ward Jr. was struck and killed by a car driven by Tony Stewart during an Empire Super Sprints race at Canandaigua (N.Y.) Motorsports Park on August 9, 2014. On Sept. 24, 2014, the Grand Jury completed its investigation and announced no criminal charges would be filed against Stewart.
Cheryl Senter, AP

Stewart drives the No. 14 Chevrolet during the Feed the Children Prelude to the Dream at Eldora Speedway on June 6, 2012 in Rossburg, Ohio. Stewart bought Eldora Speedway in 2004.
Chris Graythen, Getty Images

President Barack Obama (right) talks with NASCAR Sprint Cup Series champion Tony Stewart during an event to honor him and the other 2011 Sprint Cup Series drivers at the White House on Tuesday, April 17, 2012.
Evan Vucci, AP

Stewart, driver of the No. 14 Office Depot/Mobil 1 Chevrolet, celebrates in after winning the NASCAR Sprint Cup Series Ford 400 and the 2011 Series Championship at Homestead-Miami Speedway on November 20, 2011 in Homestead, Florida. The title was Stewart's third Cup series championship, having previously won in 2002 and 2005.
Jared C. Tilton, Getty Images

Stewart (right) celebrates atop the flag stand near fans at Daytona International Speedway after winning the 2005 Pepsi 400. According to National Motorsports Press Association (NMPA), Stewart is one of the Top 10 most popular drivers in NASCAR.
David Graham, AP

Stewart drives through the first turn at the Indianapolis Motor Speedway during the final practice session before the 85th running of the Indianapolis 500 in 2001. Stewart occasionally raced in the IZOD IndyCar series from 1996-2001.
Michael Conroy, AP

Tony Stewart (20) flies through the air after an accident during the 2001 Daytona 500. Despite winning three Cup championships and racking up 47 career wins, Stewart has yet to win a Daytona 500.
Jim Topper, AP

Stewart sits in his car in the garage area at Pocono International Raceway while talking with crew chief, Greg Zipadelli. The photo, taken in 1999, is from Stewart's rookie season in the Cup series.
Russ Hamilton, AP